Its an 04 chevy impala when i start it up in the morning and press the brake to change gear i feel a pulsation in the brake and it stops and lt is a humming or moaning sound when i brake when i drive. and also my brake pedal is spongy i have new front brakes and rotors. new struts.

You asked me in a PM if it could be the brake booster, though a possibility it does not sound like the case here. Is the ABS lamp on? If not and if it is a problem with it then it will be on shortly. Diagnosing the ABS system is not easy and you could spend a lot of money switching parts. Your current description does not sound like a wheel speed sensor so I would not worry about them right now. Since it pulses with the car still in park I would suspect either the ABS brain unit or even the ABS pump module.

My bad, Justin. I really need to stop answering these before 8AM coffee.

On the 04 LS model, ABS was a standard. It's possible that something in the system is bad, but unless the ABS and TRAC lights are going off, I'd say unlikely.

GM vehicles in the mid 2000 ranges do have a habit of having the diaphragm in the brake booster rotting out. Happened in my uncle's 04 Blazer, and Kevin's Imp that I've seen personally.

BUT!

The telltale for that is that you wouldn't get any resistance until the pedal is almost to the floor. Because it's the plunger attached to the pedal, and not the air pressure differential from the diaphragm helping to push on the master cylinder.

Soooooo...with that said.

1) Is your ABS or TRAC light on?
2) Did you check your brake fluid prior to replacing the brakes?
3) Have you checked your brake fluid recently?
4) Did you replace the brakes all the way around? Or just the front ones?
5) Have you noticed any leaks?
6) You said you feel a pulsing in the pedal. Do you actually fell any resistance?

1) Is your ABS or TRAC light on? no
2) Did you check your brake fluid prior to replacing the brakes? yes
3) Have you checked your brake fluid recently?yes
4) Did you replace the brakes all the way around? Or just the front ones? just the front rotors and brakes
5) Have you noticed any leaks? there are no leaks
6) You said you feel a pulsing in the pedal. Do you actually fell any resistance? when i start thecar when its cold it pulses when i mash it all the way down the floor then it goes away.